It's also worth changing C503 (high ESR > 20 ohms), also 47 mfd 16 volts. Others that I've changed are C543 (ESR 7.4 ohms) and C959 (ESR 4.3 ohms), again 47 mfd 16 volts. The problem might be caused by the condensers having too high a voltage rating. The rails that all these condensers are on are only 1.8 volts. The replacements I used were 100 mfd 6.3 volts as I had them in stock.